File:Bulletin 799 Plate 2B Antietam Schist photomicrograph.jpg

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Summary

Description
English: Figure caption: Antietam Schist. Porphyroblastic biotite, a, in a dolomitic matrix. The tourmaline, t, is epigenetic.
Text from the Bulletin referring to this figure: Microscopically the rock shows abundant calcite, dolomite, and biotite; some of the biotite occurs as porphyroblastic blades with inclusions of the groundmass. Quartz, albite, titanite, and pyrite are present in small amounts. Tourmaline crystals which contain inclusions of the rock minerals show that the mineral was formed as a result of pneumatolytic action subsequent to recrystallization of the rock.
Date
Source U.S. Geological Survey Bulletin 799, Geology of the McCalls Ferry-Quarryville District, Pennsylvania. By Eleanora Bliss Knopf and Anna I. Jonas. 1929. U.S. Government Printing Office, 156 p. ill. web version
Author USGS

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This work is in the public domain in the United States because it is a work prepared by an officer or employee of the United States Government as part of that person’s official duties under the terms of Title 17, Chapter 1, Section 105 of the US Code. Note: This only applies to original works of the Federal Government and not to the work of any individual U.S. state, territory, commonwealth, county, municipality, or any other subdivision. This template also does not apply to postage stamp designs published by the United States Postal Service since 1978. (See § 313.6(C)(1) of Compendium of U.S. Copyright Office Practices). It also does not apply to certain US coins; see The US Mint Terms of Use.

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